adds packaging links for Java 21

Author: David O'Sullivan

config/packaging.yml

@@ -105,6 +105,11 @@ jre-17:
   cve_notes: '[Risk Matrix](https://www.oracle.com/security-alerts/cpuoct2023.html#AppendixJAVA)'
   release_notes: '[Release Notes](https://docs.bell-sw.com/liberica-jdk/17.0.9b11/general/release-notes/)'
 
+jre-21:
+  name: OpenJDK JRE 21
+  cve_notes: '[Risk Matrix](https://www.oracle.com/security-alerts/cpuoct2023.html#AppendixJAVA)'
+  release_notes: '[Release Notes](https://docs.bell-sw.com/liberica-jdk/21.0.1b12/general/release-notes/)'
+
 jrebel_agent:
   name: JRebel Agent
   release_notes: '[ChangeLog](https://www.jrebel.com/products/jrebel/changelog)'